Progress report. New light on ethnic differences in adult lactose intolerance

An effective oral vitamin D replacement therapy in persons with spinal cord injury

BACKGROUND/OBJECTIVE

Vitamin D deficiency is prevalent in chronic spinal cord injury (SCI). A 3-month course of oral vitamin D(3) to 'normalize' serum vitamin D levels was investigated.

DESIGN

Prospective drug-intervention study.

SETTING

VA Medical Center; private rehabilitation facility.

METHODS

Seven individuals with chronic SCI and vitamin D deficiency completed 3 months of oral vitamin D(3) (i.e. cholecalciferol) supplementation. At screening, baseline, and months 1 and 3, blood was collected for serum calcium, 25 hydroxyvitamin D [25(OH)D], intact parathyroid hormone (iPTH), and N-telopeptide (NTx); 24-hour urine for calcium, creatinine, and NTx was performed. Oral vitamin D(3) (2000 IU daily) and elemental calcium (1.3 g daily) were prescribed for 90 days. The results are expressed as mean ± standard deviation (SD). Analysis of variance with a Fisher's post-hoc analysis was performed to test for differences between study visits. Subjects were classified as deficient (<20 ng/ml), relatively deficient (20-30 ng/ml), or not deficient (>30 ng/ml) in 25(OH)D.

RESULTS

Serum 25(OH)D levels were greater at months 1 and 3 than at baseline (26 ± 6 and 48 ± 17 vs. 14 ± 2 ng/ml; P = 0.005). Six of seven subjects were no longer deficient [25(OH)D >30 ng/ml] by month 3. Serum iPTH levels were significantly decreased at month 1 and month 3; serum NTx levels were significantly lower at month 3 than at baseline. Serum and urinary calcium levels remained within the normal range.

CONCLUSION

A daily prescription of 2000 IU of oral vitamin D(3) for 3 months safely raised serum 25(OH)D levels into the normal range in persons with chronic SCI on calcium supplementation.

A descriptive study on vitamin D levels in individuals with spinal cord injury in an acute inpatient rehabilitation setting

OBJECTIVE

To determine the prevalence of inadequate or severely deficient levels of vitamin D in patients with spinal cord injury (SCI) admitted to an inpatient rehabilitation service and to describe any associations between patient demographics and injury characteristics and vitamin D levels.

DESIGN

Retrospective case series.

SETTING

Academic inpatient SCI rehabilitation program.

SUBJECTS

One hundred patients with SCI who were consecutively admitted to acute inpatient rehabilitation from January to December 2007.

METHODS

Data were retrospectively abstracted from the patient's medical chart.

OUTCOME MEASURE

VitD-25(OH).

RESULTS

The prevalence of VitD-25(OH) inadequacy or severe deficiency was 93% in this sample of patients with SCI. The mean VitD-25(OH) level was 16.29 +/- 7.73 ng/mL, with a range from 7.00 to 36.80 ng/mL. Twenty-one percent of the sample had VitD-25(OH) levels that were considered as severely deficient (< or =10 ng/mL). African-American subjects had statistically significant lower mean VitD-25(OH) levels compared with Caucasian subjects (12.96 versus 17.79 ng/mL; P = .003). Persons with an incomplete injury had significant lower mean VitD-25(OH) levels compared with complete injuries (14.64 versus 18.15 ng/mL; P = .023).

CONCLUSIONS

Inadequate or severely deficient levels of VitD-25(OH) were highly prevalent in patients with SCI admitted to an acute inpatient rehabilitation service. Evaluation of serum VitD-25(OH) levels are recommended in patients with SCI because low levels may contribute to osteoporosis.

Issues in the formulation of drugs for oral use in children: role of excipients

An ideal oral drug for children should be effective, well tolerated, be of low cost and have good palatability, i.e. acceptable taste, after-taste and smell. Many of the drugs used for children are not available in suitable forms (such as chewable or liquid). Liquid forms may need to be prepared using appropriate excipients at the time of dispensing by the pharmacist. Modern medications are complex mixtures containing many other components besides the active ingredient. These are called 'inert ingredients', or excipients, and consist of bulk materials, flavorings, sweeteners and coloring agents. These excipients increase the bulk, add desirable color, mask the unpleasant taste and smell, and facilitate a uniform mixture of the active ingredient in the final marketed preparation. Unlike the active ingredients, excipients are not well regulated in most countries. Although mostly well tolerated, some adverse events and idiosyncratic reactions are well known for a variety of excipients. These components play a critical role, especially in liquid and chewable preparations that are mostly consumed by infants and children. This article reviews excipients commonly used in pediatric oral preparations.

Differential mechanism-based labeling and unequivocal activity assignment of the two active sites of intestinal lactase/phlorizin hydrolase

Milk lactose is hydrolysed to galactose and glucose in the small intestine of mammals by the lactase/phlorizin hydrolase complex (LPH; EC 3.2.1.108/62). The two enzymatic activities, lactase and phlorizin hydrolase, are located in the same polypeptide chain. According to sequence homology, mature LPH contains two different regions (III and IV), each of them homologous to family 1 glycosidases and each with a putative active site. There has been some discrepancy with regard to the assignment of enzymatic activity to the two active sites. Here we show differential reactivity of the two active sites with mechanism-based glycosidase inhibitors. When LPH is treated with 2',4'-dinitrophenyl 2-deoxy-2-fluoro-beta-D-glucopyranoside (1) and 2', 4'-dinitrophenyl-2-deoxy-2-fluoro-beta-D-galactopyranoside (2), known mechanism-based inhibitors of glycosidases, it is observed that compound 1 preferentially inactivates the phlorizin hydrolase activity whereas compound 2 is selective for the lactase active site. On the other hand, glycals (D-glucal and D-galactal) competitively inhibit lactase activity but not phlorizin hydrolase activity. This allows labeling of the phlorizin site with compound 1 by protection with a glycal. By differential labeling of each active site using 1 and 2 followed by proteolysis and MS analysis of the labeled fragments, we confirm that the phlorizin hydrolysis occurs mainly at the active site located at region III of LPH and that the active site located at region IV is responsible for the lactase activity. This assignment is coincident with that proposed from the results of recent active-site mutagenesis studies [Zecca, L., Mesonero, J.E., Stutz, A., Poiree, J.C., Giudicelli, J., Cursio, R., Gloor, S.M. & Semenza, G. (1998) FEBS Lett. 435, 225-228] and opposite to that based on data from early affinity labeling with conduritol B epoxide [Wacker, W., Keller, P., Falchetto, R., Legler, G. & Semenza, G. (1992) J. Biol. Chem. 267, 18744-18752].

"Inactive" ingredients in pharmaceutical products: update (subject review). American Academy of Pediatrics Committee on Drugs

Because of an increasing number of reports of adverse reactions associated with pharmaceutical excipients, in 1985 the Committee on Drugs issued a position statement recommending that the Food and Drug Administration mandate labeling of over-the-counter and prescription formulations to include a qualitative list of inactive ingredients. However, labeling of inactive ingredients remains voluntary. Adverse reactions continue to be reported, although some are no longer considered clinically significant, and other new reactions have emerged. The original statement, therefore, has been updated and its information expanded.

Vitamin D deficiency in veterans with chronic spinal cord injury

Chronic spinal cord injury (SCI) is associated with osteopenia, increasing the prevalence of long-bone fractures. Although disuse may be the primary cause of osteopenia, identification of any additional mechanisms of bone loss may lead to potential therapeutic interventions. We investigated the relationships of serum calcium (Ca), phosphorus (PO4), albumin, alkaline phosphatase (Alk P), and parathyroid hormone (PTH) with serum 25-hydroxyvitamin D [25(OH)D] in 100 subjects with chronic SCI and 50 control subjects. in a subgroup of 50 subjects with SCI and 50 control subjects, we correlated these parameters with serum 1,25-dihydroxyvitamin D [1,25(OH)2D]. Mean ages for the group with SCI and the controls were the same. In subjects with SCI, the duration of injury was 20 +/- 1 years (mean +/- SD). Thirty-two of 100 subjects with SCI, as compared with eight of 50 controls, had serum 25(OH)D levels less than the normal range (chi2 = 4.36, P < .05). In subjects with SCI, a negative correlation was demonstrated between serum 25(OH)D and PTH (r = .29, P < .005). Mean serum 1.25(OH)2D levels were significantly elevated in subjects with SCI as compared with controls (61 +/- 21 v 46 +/- 18 pg/mL, P < .0005). Twenty of 50 subjects with SCI had serum 1.25(OH)2D levels greater than 62 pg/mL, as compared with 10 of 50 controls (chi2 = 4.76 P < .05). A positive correlation was found between serum PTH and 1,25(OH)2D in subjects with SCI and controls (r = .41, P < .005 and r = .30, P < .05, respectively). Twelve subjects with SCI had serum PTH levels greater than the normal range. In this high-serum PTH subgroup, serum 15(OH)D concentration was significantly lower (P < .05) and serum 1,25(OH)2D and Alk P concentrations were significantly higher (P < .005 and P < .05, respectively) as compared with the subgroup with serum PTH values within the normal range. In subjects with SCI, 17 had a serum Ca concentration less than 8.5 mg/dL. In persons with SCI, depressed levels of serum 25(OH)D, as well as other factors, may result in forces inclined to reduce the serum calcium concentration. A state of mild secondary hyperparathyroidism may result, thus increasing the conversion of serum 25(OH)D to 1.25(OH)2D. These data suggest that in chronic SCI subjects, as in the general population, secretion of PTH and the increase of circulating 1.25(OH)2D are subject to control by negative-feedback mechanisms. Higher levels of serum PTH would be expected to accelerate bone resorption of a skeleton already regionally osteoporotic as a consequence of the bone mineral loss due to acute immobilization.

Substrate specificity of small-intestinal lactase: study of the steric effects and hydrogen bonds involved in enzyme-substrate interaction

Milk lactose is hydrolysed to D-galactose and D-glucose in the small intestine of mammals by the lactase-phlorizin hydrolase complex (LPH, EC 3.2.1.23-62). Lactase activity has broad substrate selectivity and several glycosides are substrates. Recently, using the monodeoxy derivatives of methyl beta-lactoside (1), we have shown the importance of each hydroxyl group in the substrate molecule concerning the interaction with the enzyme. Now we have studied the corresponding O-methyl derivatives, as well as some of the halo derivatives of 1. We have found that the enzyme presents steric restrictions to the recognition of substrates modified in the galactose moiety. In contrast, the binding site for the aglycon part of the substrate is looser. On the other hand, we have previously shown that HO-3' and HO-6 were important for the recognition of the substrate by the enzyme. Now we have found that the corresponding fluorine derivatives are not, or very poorly, recognized. This suggests that the HO-3' and HO-6 participate, as donors, in hydrogen bonds in the interaction with the enzyme.

Hypolactasia and lactase persistence. Historical review and the terminology

Lactase (more precisely lactase-phlorizin hydrolase) is located in the brush border of the small intestinal enterocytes and is responsible for the hydrolysis of dietary lactose. The earliest studies on lactase activity in mammals were published around the turn of the century. In 1903, it was found that the dog had a very low lactase activity and therefore lactose remained unhydrolysed, causing diarrhoea. Human hypolactasia was demonstrated in 1963, and it was soon found that it is very common, commoner than lactase persistence in most parts of the world. In 1973, adult-type hypolactasia was shown to be inherited by an autosomal recessive single gene. This article reviews the early expansion of the knowledge on lactase and hypolactasia as well as the correct terminology.

Genetics and epidemiology of adult-type hypolactasia

The prevalence of adult-type hypolactasia varies from less than 5% to almost 100% between different populations of the world. The lowest prevalence has been found in northwestern Europe, around the North Sea, and the highest prevalence in the Far East. The reason for the variation is that selective (primary) hypolactasia is genetically determined by an autosomal recessive single gene. It is assumed that thousands of years ago all people had hypolactasia in the same way as most mammals do today. At that time in cultures where milk consumption was started after childhood, lactase persistence had a selective advantage. Those people with lactase persistence were healthier and had more children than people with hypolactasia, and the frequency of the lactase persistence gene started to increase. The present prevalence of hypolactasia can be explained fairly well by this culture historical hypothesis. This article reviews the evidence for the inheritance of adult-type hypolactasia and the occurrence of hypolactasia in different countries and populations of the world.

Substrate specificity of small-intestinal lactase. Assessment of the role of the substrate hydroxyl groups

Lactase-phlorizin hydrolase is a disaccharidase present in the small intestine of mammals. This enzyme has two active sites, one being responsible for the hydrolysis of lactose. Lactase activity is thought to be selective towards glycosides with a hydrophilic aglycon. In this work, we report a systematic study on the importance of each hydroxyl group in the substrate molecule for lactase activity. For this purpose, all of the monodeoxy derivatives of methyl beta-lactoside and other lactose analogues are studied as lactase substrates. With respect to the galactose moiety, it is shown here that HO-3' and HO-2' are necessary for hydrolysis of the substrates by lactase. Using these chemically modified substrates, it has been confirmed that lactase does not behave as a typical beta-galactosidase, since it does not show an absolute selectivity with respect to substitution and stereochemistry at C4' in the galactose moiety of the substrate. However, the glucose moiety, in particular the HO-6, appears to be important for substrate hydrolysis, although none of the hydroxyl groups seemed to be essential. In order to differentiate both activities of the enzyme, a new assay for the phlorizin-hydrolase activity has also been developed.

4-O-beta-D-galactopyranosyl-D-xylose: a new synthesis and application to the evaluation of intestinal lactase

4-O-beta-D-Galactopyranosyl-D-xylose (2) was prepared from benzyl 2,3-O-isopropylidene-beta-D-xylopyranoside by glycosylation with 2,3,4,6-tetra-O-benzoyl-alpha-D-galactopyranosyl bromide and subsequent deprotection. Compound 2 was hydrolyzed in vitro by intestinal lactase; the Vmax was 25% of that with lactose and the Km was 370mM (cf. 27mM for lactose). Oral administration of 2 suckling rats led to urinary excretion of D-xylose which could be estimated colorimetrically.

Lactase deficiency in Singapore-born and Canadian-born Chinese

Seventy-three of 77 adult Singapore-born Chinese (95%) and 48 of 49 Canadian-born adult Chinese (98%) were demonstrated to be lactase deficient using the lactose breath hydrogen test. The similar prevalence of lactase deficiency in the Singapore- and the Canadian-born Chinese despite a larger estimated amount of daily milk ingestion in the Canadian-born Chinese (430 ml vs 157 ml) supports the concept that lactase deficiency, which is transmitted genetically, does not have an adaptable component related to the quantity of lactose ingested. When the lactose breath hydrogen test performed with a dose of 0.5 g/kg of lactose was compared with the test using a standard dose of 50 g of lactose, there was very little loss of sensitivity. In spite of the presence of lactase deficiency, only 32% of the Singapore subjects and 23% of the Canadian subjects had gastrointestinal symptoms when milk was ingested in the daily diet. Peak breath H2 was higher in females than males, but the difference was more significant in the Canadian cohort.

The human lactase-phlorizin hydrolase gene is located on chromosome 2

The lactase-phlorizin hydrolase gene was assigned to chromosome 2 by analysis of Southern blots of DNA from a panel of human-rodent cell hybrids containing characteristic sets of human chromosomes The hybridization probe used was a recently isolated cDNA clone of the human lactase-phlorizin hydrolase gene.

Purification and characterisation of amphiphilic lactase/phlorizin hydrolase from human small intestine

Human intestinal lactase/phlorizin hydrolase (EC 3.2.1.23/62) was purified in its amphiphilic form by immunoadsorbent chromatography. The purification factor was approximately 600 and the recovery 14%. The enzyme was essentially free from other known brush-border peptidases and disaccharidases and appeared homogeneous in crossed immunoelectrophoresis and polyacrylamide gel electrophoresis in sodium dodecylsulphate. The purified enzyme hydrolyzed lactose (pH optimum 5.8--6.0, Km 21 mM), phlorizin (Km 0.44mM) and other beta-galactosides and beta-glucosides. Tris inhibited the hydrolysis of lactose whereas phlorizin hydrolysis was almost unaffected. The activity against these two substrates also showed different thermal stability. It is suggested that the human enzyme has two different sites: one for lactose hydrolysis, inhibited by phlorizin and one for phlorizin hydrolysis. By gel filtration on Ultrogel AcA 34 the amphiphilic form of the enzyme had a molecular weight of 320000 while the hydrophilic form (papain-treated) had a molecular weight of 280000. This indicates that the anchoring segment(s) plus the bound detergent has a molecular weight of approximately 40000. In polyacrylamide gel electrophoresis in sodium dodecylsulphate the fully denatured enzyme had an apparent molecular weight of 160000. It is therefore suggested that the human lactase/phlorizin hydrolase is composed of two monomers each with a molecular weight of 160000. The electromicroscopic picture gives further evidence for this suggestion. In addition the possibility of a high molecular weight, one polypeptide chain is discussed.

The nutritional and physiological impact of milk in human nutrition

The nutritional value of milk as an important source of energy, high-quality protein, calcium, and riboflavin has been recognized for many years. Currently, the widespread use and promotion of milk in the U.S. as well as developing countries has been questioned. This review examines the nutrient composition of dairy products, factors that account for variability in composition of milk, milk processing, preservation, quality control, and contaminants (such as minerals, radionuclides antibiotics, microorganisms and their metabolites, herbicides, and insecticides) in milk. Consumption patterns for milk and evidence for its nutritional value, especially in children, are presented. Milk consumption has been related to disease or conditions such as atherosclerosis, milk allergy, lactose intolerance, anemia, dental problems, and others. Recent recommendations for dietary changes for individuals in the U.S. and other developed countries could affect the use of milk. In addition, the use of feeding programs in the U.S. and developing countries which are based primarily on milk has been criticized. The preparation of new types of milk designed to offset certain difficulties encountered with cow's milk are now being evaluated in humans.

The geographic hypothesis and lactose malabsorption. A weighing of the evidence

Reviewed in this article is evidence bearing on the geographic hypothesis advanced eight years ago to explain the striking ethnic or racial differences in prevalence of primary adult lactose malabsorption that are found around the world. Most evidence is found to support the hypothesis and the likelihood that some human groups came to have low prevalences of such lactose malabsorption because of selective pressures over a long historical period that favored the adult lactose absorber under particular ecological conditions.

Manifestation and occurrence of selective adult-type lactose malabsorption in Finnish teenagers. A follow-up study

In 1969--1970, a simple random sample of 129 Finnish school-aged children was examined to study selective adult-type lactose malabsorption (SLM) in this age category. SLM was found in 8 children. All subjects were reexamined 5 years later. SLM was reconfirmed in these 8 persons and found in 3 additional subjects who had normal lactose absorption in the first examination. The prevalence of SLM was 9.3%, being 8.5% in the age category 12--15 years and 9.9% in that 16--20 years. Low rise of blood glucose in the lactose tolerance test of the first examination, very low milk consumption, milk intolerance, and history of gastrointestinal symptoms were found to be of low predictive value as indicators of SLM. It was also concluded that information about dietetic sources of lactose is important to persons with SLM, but categorical exclusion of lactose from the diet is not necessary, at least in the Finnish population.

Disaccharidase activities in small intestinal mucosa in patients with cystic fibrosis

The disaccharidase activities in small intestinal biopsies were related to the morphology of the mucosa and the ages of 63 patients with cystic fibrosis and 177 healthy control subjects of Caucasian origin. In patients with CF and in the healthy control subjects under 5 years of age with normal intestinal mucosa, no low lactase activity was found. In those patients with CF who were over 5 years of age, one group had high and one group had low lactase activity, as occurs in healthy Caucasian control subjects of the same age. This finding supports the view that in patients with CF, lactase deficiency is not related to the disease entity. In patients with or without CF who had the same degree of mucosal atrophy, the decrease of disaccharidase activities followed the same pattern, indicating that enzyme activities are affected to the same extent by the damage of the mucosa. In patients with CF with pancreatic insufficiency, the disaccharidase activities were significantly (P less than 0.001) higher when compared to those in control subjects of the same age and ethnic group, although the increase was not uniform in all patients with cystic fibrosis.

Recognition of lactose intolerance

Evidence has been accumulating that except where dairying has been carried on for centuries, postweaning inability to digest milk is the norm for humans as well as other land mammals. Given the ethnic diversity of the U.S., there may well be 30 million Americans who cannot drink milk without developing symptoms and many instinctively learn to avoid it. A simple lactose tolerance test is described that establishes the diagnosis.

Relationship of lactose intolerance to milk intolerance in young children

The prevalence of lactose intolerance as revealed by the standard lactose tolerance test was compared with the occurrence of intolerance to graded amounts of milk in 69 black and 30 white children. Of the black children studied, 11% of those 4 to 5 years old, 50% of those 6 to 7 years old, and 72% of those 8 to 9 years old were found to be lactose-intolerant, yet no child was intolerant to 240 ml of milk. Symptom responses to greater amounts of milk did not suggest that the frequency of primary lactose intolerance might be a reason for limiting existing milk programs for young children. No significant differences were found between the milk intakes of black lactose-tolerant and black lactose-intolerant children, nor between milk intakes of 6- and 7-year-old black and white children in Boston. However, 8- to 9-year-old black children drank significantly less milk than 8- to 9-year-old white children did. The blood glucose response at 0, 20, and 45 min after the ingestion of 2 g lactose/kg (maximum 50 g) was unreliable as an indicator of an individual's symptomatic response to lactose.

Selection of strain, growth conditions, and extraction procedures for optimum production of lactase from Kluyveromyces fragilis

Forty-one strains of Kluyveromyces fragilis (Jörgensen) van der Walt 1909 varied 60-fold in ability to produce lactase (beta-galactosidase). The four best strains were UCD No. 55-31 (Northern Regional Research Center NRRL Y-1196), UCD No. C21(-), UCD No. 72-297(-), and UCD No. 55-61 (NRRL Y-1109). Biosynthesis of lactase during the growth of K. fragilis strain UCD No. 55-61 was followed on both lactose and sweet whey media. Maximum enzyme yield was obtained at the beginning of the stationary phase of growth. Bets lactase yields from K. fragilis UCD No. 55-61 were obtained with 15% lactose and an aeration rate of at least .2 mmol oxygen/liter per min. Supplementary growth factors were unneccessary for good lactase yeilds when yeast was grown on whey media. Best extraction of lactase from fresh yeast cells was obtained by toluene autolysis (2% vol/vol) at 37 C in .1 M potassium phosphate buffer, pH 7.0, containing .1 mM manganese chloride and .5 mM magnesium sulfate. The enzyme was concentrated and purified partially by acetone precipitation. At least 95% of the enzyme activity of the concentrated solution was retained after storage for 7 days at 22 C, for 3 wk at 4 C, and for 6 wk at -20 C.

Milk and its role in the American diet

A decline in milk consumption is postulated as a possible factor contributing to poor nutritional status. Certain common prejudices against milk may, rightly or wrongly, act as barriers to its consumption and, therefore, to its nutritional contributions. Beliefs such as "adults don't need milk;" "raw milk is better than pasteurized milk;" "nonwhite people shouldn't drink milk;" "saturated fat and cholesterol 'cause' heart disease;" "cows are ecologically unsound;" and "nutrition doesn't sell milk" can be counteracted in light of current scientific knowledge and information. It is reaffirmed that milk, in moderation, is a desirable inclusion in most people's diets.

Breath hydrogen as a diagnostic method for hypolactasia

Breath hydrogen (H2), collected by end-expiratory sampling, was measured in twenty-five patients with abdominal symptoms or diarrhoea after ingesting 50 g. of lactose. This was compared with established tests of hypolactasia. Fifteen patients with a blood-glucose rise of more than 20 mg. per 100 ml. had less than 4 parts per million (p.p.m.) rise in breath H2 at 2 hours. In contrast, ten patients with blood-glucose rises of less than 20 mg. per 100 ml. had more than a 20 p.p.m. H2 rise (mean 85.8 p.p.m. plus or minus s.d. 44.3) at 2 hours. Similarly, two patients with normal jejunal lactase activity had no significant H2 production, whereas six patients with hypolactasia had more than a 20 p.p.m. rise in H2. Symptoms related to milk or lactose ingestion were found to be unreliable. End-expiratory sampling of breath H2 would seem to be a simple, non-invasive, and accurate method of diagnosing hypolactasia, which is also very acceptable to patients. This should make it a valuable tool both in diagnostic gastroenterology and in epidemiological surveys.